Benzene, toluene and xylenes (BTX) are important aromatic hydrocarbons, for which the worldwide demand is steadily increasing. The demand for xylenes, particularly para-xylene, has increased in proportion to the increase in demand for polyester fibers and film and typically grows at a rate of 5-7% per year. Benzene is a highly valuable product for use as a chemical raw material. Toluene is also a valuable petrochemical for use as a solvent and an intermediate in chemical manufacturing processes and as a high octane gasoline component. However, in many modern aromatic complexes, some or all of the benzene and/or toluene is converted to further xylenes by either transalkylation or methylation or a combination thereof.
A major source of benzene, toluene, and xylenes (BTX) is catalytic reformate, which is produced by contacting petroleum naphtha with a hydrogenation/dehydrogenation catalyst on a support. The resulting reformate is a complex mixture of paraffins and the desired C6 to C8 aromatics, in addition to a significant quantity of heavier aromatic hydrocarbons. After removing the light (C5−) paraffinic components, the remainder of reformate is normally separated into C7−, C8 and C9+-containing fractions using a plurality of distillation steps. Benzene can then be recovered from the C7−-containing fraction to leave a toluene-rich fraction which is generally used to produce additional C8 aromatics by either methylation or transalkylation with part of the C9+-containing fraction. The C8-containing fraction is fed to a xylene production loop where para-xylene is recovered, generally by adsorption or crystallization, and the resultant para-xylene depleted stream is subjected to catalytic conversion to isomerize the xylenes back towards equilibrium distribution and to reduce the level of ethylbenzene that would otherwise build up in the xylene production loop.
While catalytic technologies are becoming more efficient in achieving the desired chemical reactions to maximize para-xylene production while reducing loss of valuable aromatic molecules, there is a continuing need to achieve savings in hardware cost and energy consumption so as to reduce the overall para-xylene production cost.